1. Technical Field
The invention relates generally to devices that provide moveable work platforms underneath a bridge and, more particularly, to devices that permit work platforms to be moveably suspended from the underside of a bridge. Specifically, the invention relates to a suspension device that provides a pair of rails clamped to the lower webs of parallel bridge girders, with a scaffold member being rollably mounted on each rail, and with the work platform being built upon and extending between the two scaffold members.
2. Background Information
Bridges are used for numerous purposes in modern society. Bridges often carry roadways or railroad tracks over natural obstacles such as rivers and valleys and are also used as overpasses to permit one roadway to cross another without intersection. Bridges thus facilitate the uninterrupted flow of traffic along roadways and railways.
Many bridges, particularly those upon which automobiles and trucks travel, provide a roadway surface at the top thereof. Such bridges typically include a plurality of piers extending vertically upward from the natural obstacle or roadway to be traversed by the bridge, a plurality of horizontal parallel and spaced apart girders supported on top of the piers and extending between the piers and to the grade adjacent the terminal ends of the bridge. A roadway, typically constructed of concrete, is constructed on top of the girders. Bridges may also include trusses and suspension systems in addition to or in the alternative to piers. The design and construction of such bridges is well known and understood in the relevant art.
Bridges also typically require periodic maintenance to ensure their continued structural stability and utility. Bridges having a roadway at the upper surface thereof often require maintenance of the roadway surface at least as often as conventional roadway surfaces that are constructed above grade. More particularly, bridge roadway surfaces often require more frequent maintenance inasmuch as such roadways experience higher mechanical stresses than non-elevated roadways. Such enhanced mechanical stresses occur due to the loading that results from supporting a roadway across parallel and spaced girders instead of from a continuous roadbed, as well as due to the quicker thermal expansion and contraction that results from both the upper and lower surfaces of the roadway being exposed to the atmosphere. Such bridge-borne roadways thus require frequent maintenance and are sometimes in need of complete replacement.
The replacement of a bridge-borne roadway begins with the complete removal of the old roadway. Such removal occurs with the use of jackhammers and heavy equipment to completely remove the roadway until only the girders remain, the girders being supported by piers and/or other support structures. Planar construction forms are then installed in the spaces between the girders such that the construction forms and the girders together constitute a single generally planar surface upon which the roadway can be constructed. The new roadway is constructed on the surface by constructing a network of steel reinforcement rods a few inches above the surface and then by pouring concrete over the surface to encapsulate the reinforcement rods in the concrete.
Once the concrete roadway has cured, the construction forms must be removed from the underside of the roadway. Inasmuch as the new roadway extends across the top of the bridge, with the girders and construction forms being underneath the new roadway, the construction forms must be removed from the underside of the bridge. Inasmuch as the bridge is elevated above a natural obstacle or another roadway, the workmen removing the construction forms must stand upon an elevated work platform that is supported either by a scaffolding or other structure from below or is suspended by a structure attached to the underside of the bridge. Such an elevated work platform must be readily moveable to allow the workmen to reach all areas of the underside of the bridge, and must additionally be secure enough to prevent the workmen from falling. While ground-based support structures such as scaffolding and scissor platforms provide excellent stability and safety, the utility of such devices is limited inasmuch as most bridges traverse natural obstacles such as rivers or extend over roadways that must continue to carry traffic. As such, a support structure that suspends the work platform from the underside of the bridge provides the most versatility in removing the construction forms.
One type of structure for supporting a work platform from the underside of a bridge is presented in U.S. Pat. No. 5,839,539 to Smith. Smith discloses a support structure that includes a plurality of hangers that are positioned at the lower web of a girder, with each hanger including an upward-facing roller. Once each of the hangers is adjusted such that the rollers are each at a common height, a scaffolding member having an inverted U-shaped channel is installed onto a plurality of the rollers such that the rollers are received within the U-shaped channel. While the structure disclosed in Smith has achieved limited success for the objectives presented therein, the Smith device has not been without limitation.
As an initial matter, the hangers disclosed in Smith do not clamp directly to the web at the underside of the girder, but rather hang loosely from the lower web without being clamped thereto. In operation, it is anticipated that the scaffolding member will roll along the rollers from one hanger to another to allow the platform carried by the scaffolding member to move along the length of the bridge. One problem associated with the Smith device, however, is that a minor maladjustment in the hanger can cause the scaffolding member approaching one of the rollers to strike the roller instead of rolling smoothly over the top of the roller. Such a strike often results in the hanger being pushed out of alignment with the other rollers inasmuch as the hanger is not securely clamped to the web of the girder. Additionally, the adjustment of each of the hangers in an attempt to align each of the rollers is both time consuming and often ineffective inasmuch as the hangers are only loosely supported from the girders and are not securely clamped thereto.
The looseness of the hangers often requires a user to install successive hangers onto the girders as the scaffold member is advanced. More specifically, the successive hangers are installed by workmen reaching in the forward direction off the scaffold member to install a successive hanger onto the girder, with the workmen then advancing the scaffold member to roll along the newly installed successive hanger. Such a methodology is known in the relevant industry as "leapfrogging" and is both labor intensive and slow inasmuch as the hangers are not all installed in a single procedure. While the hangers of the Smith reference could, potentially, all be installed in a single procedure, the loose support of the hangers often results in one or more hangers falling from the girder due to wind, vibration, and other typically encountered phenomena. As such, as the scaffold member is moved along the underside of the girders, with the hangers being removed from behind the scaffold member after the scaffold member has traversed them and then being reinstalled ahead of the scaffold member to permit the scaffold member to incrementally move in the forward direction. Inasmuch as the hangers are removed after the scaffold member has passed over them, the movement of the scaffold member cannot be reversed unless the hangers are reinstalled in a reverse-leapfrogging fashion.
Additionally, inasmuch as the hangers of the Smith reference align with the opposite edges of the lower web of the girder, a junction plate extending between the ends of girders butted together creates special problems for the Smith hanger inasmuch as such extension plates often protrude outwardly from the edges of the lower web. In such a circumstance, the rollers of the hangers adjacent the junction plate will be misaligned with the other hangers on the girder. Alternatively, each of the hangers can be spaced the same distance away from the edges of the lower web to ensure that the rollers traversing the junction plate are aligned with all of the other rollers. Such a solution causes the hangers to be even more loosely attached to the girder, increasing the likelihood that the hangers will become knocked into misalignment due to contact between the scaffold member and each successive roller. Such misalignment prevents the scaffold member from rolling along the rollers, and can potentially result in the work platform falling from the bridge structure.
The need thus exists for an improved structure to suspend a work platform below a bridge girder. Such an improved structure preferably would provide a track that is securely clamped to the lower web of one or more bridge girders and a scaffold member having a plurality of rollers that roll along the upper surface of the track, with the scaffold member supporting the work platform thereon.